360 COBLENTZ: BISMUTH THERMOPILES 



Reduction of the gas pressure to 0.1 mm. pressure eliminates 

 air currents and doubles the sensitivity. 



Owing to the high sensitivity of this device, it would seem de- 

 sirable to attach it to a recording device and test its usefulness 

 for measuring solar radiation at the earth's surface and at the 

 highest altitudes attainable with a balloon. Its application to 

 the radiomicrometer (loc. cit) is also important. In this connec- 

 tion it would seem desirable to construct the device in accordance 

 with the resistance requirements for critical damping in moving 

 coil galvanometers rather than adhering to the older theory worked 

 out by Boys which requires but a single turn of wire and a single 

 thermoelement. 



The application of such instruments to the measurement of 

 radiation from stars, fireflies, etc., seems futile, unless absorption 

 screens are used to determine the quantit^y of radiation in differ- 

 ent parts of the spectrum. Otherwise the measurement is but 

 little more than a test of the sensitivity of radiometer. 



